1. Field of the Invention
Embodiments of the invention relate to a fuse circuit. More particularly, embodiments of the invention relate to an e-fuse circuit using a transistor leakage current path.
2. Description of the Related Art
Fuse circuits are regularly included with semiconductor circuits for a number of different reasons. For example, many semiconductor memory circuits include a collection of fuses as part of circuitry enabling memory redundancy. In this context, it is well known that memory devices, such as Dynamic Random Access Memory (DRAM), are manufactured to include a large number of memory cells. Should only a few of these memory cells be defective, the entire memory device is often considered unusable. Thus, the consistent appearance of only a few bad memory cells in a much larger array of memory cells will adversely affect manufacturing yield for the memory device. As a result, provision for a number of redundant memory cells adapted to replace the defective memory cells identified in a memory device is commonly made.
In another example, fuses are also used within a semiconductor device to implement electronic identification for the device. So-called “electronic chip identification” provides reference information for the device, such as location coordinates for the device within a wafer being fabricated. By resort to this reference information, a manufacturer may also search manufacturing data related to a particular semiconductor device.
Conventional fuses are made of polysilicon or metal, and a programming circuit is typically required to control a conductivity state (e.g., open or short) for the fuse circuit, regardless of its material composition.
Various conventional techniques have been used to program a fuse. These techniques include selectively applying an over-current to the fuse, or directing a laser beam onto a coupling connection for the fuse, etc. Conventional techniques that selectively direct a laser beam in order to program the conductivity state of a fuse are widely used because of their high reliability and simplicity. However, such programming techniques do not provide an ability to repair a memory device once it is placed into a package.
This type of limitation resulted in the development of an electronic fuse (“e-fuse”). The use of e-fuses allows a fusing operation to be performed at the package level of a semiconductor device (e.g., at a fabrication stage following the assembly process). The conductivity state of an e-fuse has been conventionally defined by melting a fuse coupling, by defined electrical carrier migration, etc. Many of thee techniques are accomplished by selectively applying an electrical bias voltage or current to a fuse to vary its conductivity. For example, a program voltage Vpgm and a program current Ipgm may be supplied to a fuse for a predetermined programming period in order to define its conductivity state. As a result of these applied bias signals, electrical carriers may migrate from one or more fuse components to thereby vary the electrical resistance of the fuse. In various conventional examples, the fuse will exhibit either a short circuit condition or a highly resistive condition.
A conventional e-fuse is disclosed, for example, in Korea Patent No. 0363327. In this type of e-fuse, a resistance ratio between the fuse resistance and a reference resistance is detected by a latch type sensor. In order to establish a desired resistance ratio, the e-fuse must be subjected to a defined program current for a predetermined programming period in order to maintain reproducibility and reliability of the fuse programming operation.
Unfortunately, consistent (i.e., highly reliable and reproducible) programming results are sometime difficult to obtain, since a fuse's response to an applied program current may vary in accordance with certain fabrication process variations. Thus, if a relatively excessive program current is applied, heat may be generated in and around the fuse before the fuse is properly programmed. This heat may damage certain layers of the semiconductor device and/or result in low reproducibility and reliability of the fuse programming operation.
Therefore, a demand exists for an e-fuse and related method of programming that produces greater reproducibility and increased reliability. Fuse programming should not be subject to variable influences resulting from variations in the fabrication processes used to make the fuse. The structure of the e-fuse should enjoy considerable immunity to relatively high programming voltages and/or relatively excessive programming current.